With the Democrats now holding the majority in the House of Representatives, Mr Trump appears to be worried about what could emerge.

He has long raged against Special Counsel Robert Mueller’s investigation into alleged collusion between Mr Trump’s presidential campaign team and Russia in 2016.

The President is particularly worried the “witch hunt” — which has already led to criminal charges against several of his associates — could extend to scrutiny of his finances.

Donald Trump is in panic mode after the Democrats took control of the House of Representatives, exposing him to deeper investigation. Picture: Jim Watson/AFPSource:AFP

WHY HAS SESSIONS GONE?

The Republican-led House Intelligence Committee had protected Mr Trump from a more expansive investigation into his campaign. But new chair Adam Schiff is likely to want more action and to ensure Mr Mueller can complete his investigation into Russian election interference unimpeded.

Mr Trump has spent the past year attacking “weak” Mr Sessions for removing himself from the probe, after Democrats accused the Attorney-General of failing to disclose his contacts with the Russian ambassador as a senior adviser to Mr Trump’s campaign.

The President blamed Mr Sessions for failing to protect him from the investigation.

“What kind of man is this?” Mr Trump fumed on Fox News in August, saying the Attorney-General “never took control of the Justice Department”.

Mr Sessions argued the department would “not be improperly influenced by political considerations”.

Mr Whitaker has been critical of Mr Mueller’s investigation, and could now take over oversight of the probe from Deputy Attorney-General Rod Rosenstein.

Many fear this could enable Mr Trump to effectively kill off the investigation.

Mr Sessions submitted his resignation yesterday, in a letter delivered to the White House. The former senator and early Trump supporter made it clear it was not his decision.

Jeff Sessions said he had been determined to do his duty and serve his country, and had ‘done so to the best of my ability’. Picture: Ho/US Department Of Justice/AFPSource:AFP

“Dear Mr President, at your request I am submitting my resignation,” he wrote. “I came to work at the Department of Justice every day determined to do my duty and serve my country. I have done so to the best of my ability.”

Former Justice Department spokesman Matt Miller said Mr Whitaker was the “worst possible choice” for “anyone who wants to protect the integrity of the Mueller investigation.”

He said the Acting Attorney-General was “one of the few people at the Justice Department who’s weighed in on the record criticising the Mueller investigation,” adding, “I don’t think that’s a coincidence.”

Former judge Andrew Napolitano told Fox News the Democrats wanted to run “shadow investigations” into Mr Trump, exposing information Mr Mueller has so far kept from the public.

“The President can fire an Attorney-General for almost any reason, but not for an improper purpose,” he said. “He cannot fire him if the purpose of the firing is to shake up the leadership of the Justice Department in order to interfere with a criminal investigation.”

Judge Napolitano said the situation was “beginning to look more and more nefarious”.

Mr Trump is particularly concerned with limiting the inquiry’s scope, something Mr Sessions would not do.

In July last year, the President told The New York Times that any investigation into his finances by Mr Mueller would be crossing a “red line”.

Journalist Bob Woodward’s book Fear: Trump In The White House recounts how Mr Trump reacted when he learnt that Mr Rosenstein had appointed Mr Mueller.

“Trump’s mood deteriorated overnight and the next day, May 18, was the worst,” Woodward writes. “The President erupted into uncontrollable anger, visibly agitated to a degree that no one in his inner circle had witnessed before. It was a harrowing experience.”

The President stormed through the White House, the journalist continues.

“I didn’t hire him for the FBI,” Mr Trump said, according to West Wing staff. “Of course he’s got an axe to grind with me.

Some fear Donald Trump fired Jeff Sessions in order to kill off Special Counsel Robert Mueller’s Russia probe. Picture: Saul Loeb/AFPSource:AFP

He asked an aide what powers a special counsel had, according to Woodward, and was told Mr Mueller would have “virtually unlimited” scope.

“Now I have this person, who has no accountability, who can look into anything, however unrelated it is?” Mr Trump reportedly said. “They’re going to spend years digging through my whole life and finances.

“They’re out to get me. This is an injustice. This is unfair. How could this have happened? It’s all Jeff Sessions’ fault. This is all politically motivated. Rod Rosenstein doesn’t know what the hell he is doing. He’s a Democrat. He’s from Maryland.

“I’m getting punched. I have to punch back. In order for it to be a fair fight, I have to be fighting.”

MSNBC’s Nicolle Wallace said “every tax return, every scandal” could now be examined.

Her colleague Kurt Bardella said five members of Mr Trump’s Cabinet — Ryan Zinke, Ben Carson, Betsy DeVos, Kirstjen Nielsen and Wilbur Ross — could face fresh pressure from the House Oversight Committee.

“For the better part of the last two years, the House Oversight Committee has gone dormant,” Mr Bardella wrote. “Chairman Trey Gowdy hasn’t sent a single subpoena to the Trump administration.

“Democrats, however, will have no such hesitation.”

WHAT WILL HAPPEN NOW?

Mr Trump’s acting Attorney-General is on his side. In August 2017, Mr Whitaker wrote on CNN that looking into Mr Trump’s personal finances, or those of his family, “goes beyond the scope of the appointment of the special counsel”.

Mr Whitaker, a conservative legal commentator before he joined Mr Sessions’ staff, last year suggested making Mr Mueller’s budget “so low that his investigation grinds to almost a halt”.

He also defended Mr Trump’s son, Donald Jr, for meeting with Russians at Trump Tower in the hope of securing dirt on Hillary Clinton in 2016.

“You would always take that meeting,” he said.

The meeting, and the Trump family’s attempts to keep it secret, have been a focal point for the investigation.

Nancy Pelosi, who leads the Democrats in the House of Representatives, called Mr Sessions’ firing a “blatant attempt” to undermine the probe.

Given his record of threats to undermine & weaken the Russia investigation, Matthew Whitaker should recuse himself from any involvement in Mueller’s investigation. Congress must take immediate action to protect the rule of law and integrity of the investigation. #FollowTheFacts

She said Mr Whitaker should follow in Mr Sessions’ footsteps and recuse himself from the Russia probe.

Mr Whitaker’s associates told The Washington Post he would not be doing so — and would not approve a subpoena of Mr Trump.

Democratic party Senate leader Chuck Schumer said: “Clearly, the President has something to hide.”

Even some Republicans appear to have shared the Democrats’ concern over the future of the inquiry, with Senator Susan Collins and Mitt Romney saying it should not be impeded.

Russia insisted Mr Sessions’ firing would have no affect on the Mueller probe, while White House counsellor Kellyanne Conway said the sacking was “not a constitutional crisis”.

Asked whether Mr Trump had instructed Mr Whitaker to limit the investigation, she said: “(The) President hasn’t instructed him to do anything.”

Mr Trump now needs a permanent replacement for Mr Sessions. He is reportedly considering former New Jersey Governor Chris Christie and Florida Attorney-General Pam Bondi, sources familiar with the matter told CNN.

Mr Christie, a former lawyer, could face calls to recuse himself like Mr Sessions, since he was a 2016 campaign surrogate for Mr Trump. Ms Bondi could also be a controversial choice because of a $US25,000 ($A34,000) gift she received from Mr Trump’s foundation during her 2016 re-election campaign.

The nominee will need to be confirmed by a vote in the Senate — a process that should be made easier by the Republicans’ seat gains.

Congressman Jerry Nadler, incoming House Judiciary Committee chairman, said the sacking fitted a “clear pattern of interference” from Mr Trump.

“There is no mistaking what this means, and what is at stake. This is a constitutionally perilous moment for our country and for the President,” Mr Nadler said.

“Donald Trump may think he has the power to hire and fire whomever he pleases, but he cannot take such action if it is determined that it is for the purposes of subverting the rule of law and obstructing justice.

“If he abuses his office in such a fashion, then there will be consequences.”

Mr Nadler said it would be “inappropriate” for Mr Whitaker to supervise the special counsel investigation.

The President also yesterday threatened to try another tactic to stop the Democrats digging too deep — launching an investigation of his own into “leaks” and “much else” through the Republican-controlled Senate.

If the Democrats think they are going to waste Taxpayer Money investigating us at the House level, then we will likewise be forced to consider investigating them for all of the leaks of Classified Information, and much else, at the Senate level. Two can play that game!

According to NBC News, Voters Nationwide Disapprove of the so-called Mueller Investigation (46%) more than they Approve (41%). You mean they are finally beginning to understand what a disgusting Witch Hunt, led by 17 Angry Democrats, is all about!

Meanwhile, Mr Mueller — a Republican — will be trying to ensure his findings are revealed, with his team now writing a final report. Mr Trump was said to be reviewing his written answers as he prepared to fire Mr Sessions.

The President cannot directly sack the special counsel. But Mr Sessions’ replacement will have the power to do so, or end the inquiry.

Mr Whitaker has called on Mr Rosenstein to “order Mueller to limit the scope of the investigation” or risk the inquiry starting “to look like a political fishing expedition”.

Mr Rosenstein, also a Republican, appointed Mr Mueller to lead the inquiry after Mr Trump fired FBI director James Comey in 2017.

There has also been a question mark over Mr Rosenstein’s future since it was alleged he had discussed invoking a constitutional clause to oust Mr Trump.